1. Field of the Invention
The present invention relates to a vehicle-use generator, and more particularly to a vehicle-use generator including tandem rotor cores each of which has claw-shaped magnetic pole cores around which a field coil is wound.
2. Description of Related Art
There is known a vehicle-use generator having a tandem rotor structure in which two Lundell type rotors are tandem-connected (may be referred as a tandem type vehicle-use generator hereinafter), as disclosed, for example, in Japanese Patent Application Laid-open Nos. 1-157251, 5-137295, and 5-308751. Such a tandem rotor structure makes it possible to provide a compact and low-cost vehicle-use generator capable of outputting two different generation voltages that can be regulated individually. In other words, the tandem rotor structure makes it possible to greatly reduce the manufacturing cost and installation cost of a vehicle-use generator compared to a case where two different vehicle-use generators are installed separately.
However, such a tandem type vehicle-use generator has a problem in that a regulation speed of its generation voltage is slow, because the excitation circuit of the Lundell type rotor structure in which a field coil having a large number of turns is wound around claw-shaped pole cores exhibits a considerably large inductance, and accordingly exhibits a considerably large excitation time constant. This makes it difficult to keep the generation voltage at its target regulation voltage by adjusting an excitation current, when a consumption current of an electric load varies rapidly.